You need to get the SAS Amadeus PNR, which is different from the UA PNR. If you call UA then they can give it to you, or maybe you have to call SAS.
Good luck with calling SAS in the near future......
Oh, if you have the Amadeus PNR then you can stick it into
www.checkmytrip.com and it will give you the United PNR, but that doesn't help in the reverse case. I guess this is one reason that I book with SAS but that is a mistake that I won't make again given the ash scenario.